Sunlight is the term used for the Sun's starlight observed during daytime. During nighttime, albedo describes solar reflections from other Solar System objects including moonlight.

Observation and measurement of starlight through telescopes is the basis for many fields of astronomy,[2] including photometry and stellar spectroscopy.[3] Starlight is also a notable part of personal experience and human culture, impacting a diverse range of pursuits including poetry,[4] astronomy,[2] and military strategy.[5]

The US Army spent millions of dollars in the 1950s and onward to develop a starlight scope, that could amplify starlight, moonlight filtered by clouds, and the fluorescence of rotting vegetation about 50,000 times to allow a person to see in the night.[5] In contrast to previously developed active infrared system such as sniperscope, it was a passive device and did not require additional light emission to see.[5]

Starlight spectroscopy, examination of the stellar spectra, was pioneered by Joseph Fraunhofer in 1814.[3] Starlight can be understood to be composed of three main spectra types, continuous spectrum, emission spectrum, and absorption spectrum.[1]